The present invention relates generally to non-contact gauging systems and, more particularly, a robot-based gauging system and method for determining three-dimensional measurement data of an object.
Demand for higher quality has pressed manufacturers of mass produced articles, such as automotive vehicles, to employ automated manufacturing techniques that were unheard of when assembly line manufacturing was first conceived. Today, robotic equipment is used to assemble, weld, finish, gauge and test manufactured articles with a much higher degree of quality and precision than has been heretofore possible. Computer-aided manufacturing techniques allow designers to graphically conceptualize and design a new product on a computer workstation and the automated manufacturing process ensures that the design is faithfully carried out precisely according to specification. Machine vision is a key part of today's manufacturing environment. Machine vision systems are used with robotics and computer-aided design systems to ensure quality is achieved at the lowest practical cost.
In a typical manufacturing environment, there may be a plurality of different non-contact sensors, such as optical sensors, positioned at various predetermined locations within the workpiece manufacturing, gauging or testing station. In order to obtain three-dimensional measurement data using a two-dimensional non-contact sensor, the sensor may be moved in relation to the workpiece. Therefore, it is important to know the exact location and orientation of the moving item (either the sensor or the workpiece) each time the sensor acquires image data of the workpiece. This tends to be fairly straightforward for accurate motion devices (e.g., a CMM), since the reported position reflects the actual position of the device. The motion controller of an accurate motion device may include various compensation factors that get applied to the motion control to ensure the commanded position matches the actual position of the device. However, the high cost associated with these types of motion devices is prohibitive to them being used in a typical manufacturing environment.
As an alternative to these more expensive motion devices, it is possible to use a conventional industrial robot as the motion device in the gauging system. By affixing the non-contact sensor to the industrial robot, the robot can be used to move the sensor in relation to the workpiece. Industrial robots are well suited to perform complex motion sequences which are customized for the workpiece. In addition, many standard industrial tools are available which allow the programming of the motion sequences to be performed off-line and subsequently downloaded to the robot controller.
The problem with a robot-based gauging system is that the conventional industrial robot is not an inherently accurate motion device. Robot controllers generally utilize ideal kinematic models when instructing robot motion. The physical characteristics of the robot arm vary slightly from the ideal model, and thus the actual movement of the robot arm varies slightly from the commanded motion sequence. Furthermore, these physical characteristics are likely to change as the robot is subject to wear and thermal changes. Most robot controllers are not equipped with any additional means for translating and/or correcting the reported position into an actual position of the robot arm. As a result, conventional industrial robots have not heretofore been used in non-contact gauging systems and other highly accurate manufacturing workstation applications.
To this end, the robot-based gauging system of the present invention accurately determines three-dimensional measurement data for a workpiece through the use of a synchronized scanning process without the need for an expensive motion device, such as a CMM.
The gauging system includes a robot having at least one movable member and a robot controller for controlling the movement of the movable member in relation to the surface of an object. A non-contact sensor is coupled to the movable member of the robot for capturing image data representative of the surface of the object. A position reporting device is used to report position data representative of the position of the non-contact sensor. In addition, a synch signal generator is used to generate and transmit a synch signal to each of the non-contact sensor and the position reporting device, wherein the non-contact sensor reports image data in response to the synch signal and the position reporting device reports position data in response to the synch signal.
The gauging system further includes a vision system adapted to retrieve image data from the non-contact sensor and position data from the position reporting device. As the non-contact sensor scans the surface of the object, there is a time latency between when the sensor strobes its laser to when processed image data is available to the vision system. In other words, the image data reported by the sensor lags in time behind the position data reported by the position reporting device. Therefore, the vision system must be able to synchronize the image data with the position data. A memory storage space is used to store position data so that the vision system can synchronize the image data with the position data. In this way, the robot-based gauging system of the present invention is able to quickly and accurately determine three-dimensional measurement data for the object.
For a more complete understanding of the invention, its objects and advantages, reference may be had to the following specification and to the accompanying drawings.